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- most simple example : the rays of the sun
-It can't be seen but can be felt as heat : objects absorb the rays and slowly restore it as heat (ex: surface of the earth at night).
-this property is used to :
*make house heaters , the recent ones are integrated in the walls or in the floor and unlike the others , they create warmth in the structure of the house (instead of inside it).
*detect if a construction is well insulated thanks to a color scale (thermography) .

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Devices and techniques that use IR (Sabine & Caroline)

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Devices and techniques that use IR (Sabine & Caroline)

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- thermography : creates images based on the differences in surface temperature by detecting infrared radiations that emanates from objects and their surrounding environment
- night vision devices (NVD) : create image by converting ambient light photons into electrons that are then amplified by an electrical and chemical process and then converted back into visible light. They may have an IR illuminator making it an active NVD.
- IR data transmission : used in short range communication between many common devices (ex : TV remote controller). The equipement that received the light interprets it according to a code and then switch on or off for example.
- spectroscopy IR : is a method to identify bonds in molecules, each chemical bond vibrates at a caracteristic frequency allowing us to determine which bond it is.
- Active Autofocus : camera uses infrared sensors to adjust the focus. The camera is sending away infrared radiation and is recording the time it takes to come back. You have probably seen this system : when using active autofocus, cameras are not only sending infrared light but also red light that you're able to see.

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- Refraction :

Refraction has an important affect on waves that travel through Earth.

Except for love and rayleigh waves, the seismic velocity increase with depth and refraction of waves causes the path followed by body waves to curve upward.

- reflection :

Reflection, it is like sound waves that are reflected like an echo or light waves that reflected in a mirror.

They are used to prospect for petroleum and investigate Earth's internal structure.

There is a reflection when a wave hits a change of the rock (usually with a change of the seismic wave speed.)

A part of the energy carried by the incident waves is transmitted through the material and an other part is reflected back into the incident wave.

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The advantages and disadvantages of G.P.S

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The advantages and disadvantages of G.P.S

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III - Advantages of G.P.S :

The navigators save a lot of time and are more precise on their current position because the G.P.S system indicates the latitude, and the longitude (and also the altitude) exact to the meter or even 10 cm for some satellites.

The speed of electromagnetic waves and their constant emission from a satellite allows real-time geolocalisation.

This service is free for smartphone, which has allowed a wide development of this system (if it had been paid it would probably have been less developed).

The G.P.S can also track stolen vehicles

IV - Disadvantages of G.P.S :

These waves pass through the atmosphere, but are blocked by rigid obstacles like mountains or buildings and that is why sometimes geolocalisation does not work, or in part only. Cloud can also interfere with waves if they are in high concentration.

The United-States can decide to suspend its service or given bad information.

If there is a major problem with the satellites humans no longer know how to use a map.

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The Wave Power Plant of Mutriku, in Spain

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The Wave Power Plant of Mutriku, in Spain

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This is a surface plant, precisely a dam comprised of 16 turbo alternators in 16 chambers, which are blank of air. When the water gets inside the chambers, it pressures the air, making the turbine rotating, and creating current with eletromagnetic induction. The aspiration effect of the air when it is leaving the chambers also generates electricity. This is more interesting than wind turbines, because they are less expansive and this can help saving more than 300 tons of CO2 each year to replace the usage of fossil energies.

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The principle is about multiple motion-sensitive cylinders, connected together by hinges, recieving the mechanical energy of the swell (movement of water). The fact that this concept uses the wave curvature, and the fact that waves breaks natually over time makes that you need to place it at good range from the coast. The pros are that this makes low junks when the device reaches end of life : we can sink it directly in the sea and it creates an artificial reef. The energy produced every year is about 750kW??? making this supply over 500 homes per device. But the problems are if you place the device enough far from the coast to get great waves, the price of the Watt will be very high. And the biggest problem is that this blocks the path of boats.

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I. What are the different ways waves are created ?

1. Basic waves

To begin waves on the sea are mechanical waves and are caused by transversal waves. Basic waves are created by energy passing through water causing it to move in a circular motion. Waves transmit energy across the ocean, not water. They are most commonly caused by wind. Wind-driven waves or surface waves are created by the friction between wind and surface of water. These types of waves are found globally across the open ocean and along the coast.

2.Dangerous waves

Hurricane:
The strong winds and pressure from this type of severe storm causes storm surge, a series of long ways that are created far from shore in deeper waterand intensify as they move closer to land.

Tsunamis:
They are caused by underwater disturbances that displaces a large amounts of water quickly such as earthquakes, landslides or volcanic eruptions.

Tidal waves:
They are caused by the gravitational pull of the sun and the moon. These waves are tides so we call them Tidal waves. It is a common misconception that a tidal wave is also a tsunami but the cause of tsunamis are not related to tide information at all.

II. How can we use the waves ?

Waves on the sea are most commonly used to create energy in power plants. We have 2 examples :

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1. The G.P.S works thanks to satellites sent into space via rockets. This system works as follows : Each place on Earth is flown over by at least 4 satellites at the same time, which allows a device to geolocate itself as follows.

2. The 3 satellites send to the device a signal, containing the time of emission of the signal, by the satellite, when the device receives these signals, it notes the time at which it received them, and it decodes in these same signals the time at which they were issued.

3. The phone therefore knows the time it takes for the signals to come from the satellites, and since it knows the speed of the signal, these are waves that travel at the speed of light, and in a vacuum, the phone can therefore calcuate the distance that separates it from the satellites. (D=V*T   D : distance / V : speed / T : time)

4. The device can therefore calculate its distance from the satellites that fly over it, it can position itself. This is called trilateration, which is what you can do with three satellites.

5. The fourth satellite is used to synchronize the clock of the satellites, and the clock of the device, because the satellites have a very precise atomic clock, which the device does not. Since the G.P.S system is based on a measurement of time, all the clocks must be synchronized to the nearest billionth of a second, and this is useful because an error of 3 billionth of a second in the measurement of time is an error of 1 meter in the location.

6. But to determine the position of a device in relation of the satellites, it is necessary to know the position of the satellite in relation to the Earth, these are the control centers and the stations, a network of antennas able of receiving, and of transmitting signals that indicate to satellites its location relative to the Earth.

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- wavelenght : from 800*10⁻⁹ m to 10⁻³ m

- frequency : from 3*1011 Hz to 3*10¹⁴ Hz
- atom absorbing energy then releasing it    ->IR
- discovered in the 19th century by (astronomer) Herschel , he put thermometers in the path of each color from de uv light spectrum + one after the red : each one had a different temperature including the one after red --> IR

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II)  Different types of waves (Zoé Lilou)

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II)  Different types of waves (Zoé Lilou)

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. they're formed acording to different weather condiions
. they are categorized based on their formation and behaviour

BREAKING WAVES
. formed when the waves collapses on top of itself
. a wave can breaks anywhere on the surface of water, but     most commonly on a coastline since wave heights are                      amplified in less deep water areas

SPILLING WAVES
They're formed at gentle inclinations of the ocean floor. They take more time to break as compared to other types

PLUNGING WAVES
It is when waves pass over an inclined ocean floor, the wave curls itself and trap a pocket of water underneath it.

SURGNG WAVES
They are produced when swells reach shorelines haing a steep profile.

COLLAPSING WAVES
They are a mix between punging waves and surging waves.

DEEP WATE WAVES
They're are formed in areas where the depth of the water is more than half of the wavelength of the wave.

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III) Differences between Mediteranean sea and Atlantic Ocean (Zoé Lilou)

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III) Differences between Mediteranean sea and Atlantic Ocean (Zoé Lilou)

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III) Differences between Mediteranean sea and Atlantic       Ocean

MEDITERANEAN SEA
. closed basin
. the amplitude of the tide is not as visible as along the coasts of Atlantic
. waves rarely exceed 6meters and the wavelenght is 3 times less than in the ocean

ATLANTIC OCEAN
.the height can vary from a few centimeters to around 30 meters
.the oceanic coasts can receive swells thathave traveled thousands of kilometers

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I - What is G.P.S ?

The G.P.S (Global Positioning System) was originally designed by the Federal Government of the United States for military purposes.

The G.P.S system works with electromagnetic waves, divided into 2 frequencies v1 (1575 MHz) and v2 (1227 MHz)

The system was subsequently developed by other countries such as China with Beidu system, Russia with its Glonass system, or even Europe with its Galileo constellation which has 30 satellites, 26 of wich are operational being located at 23 000 km above the Earth. These satellites are spread over 3 differents orbits.

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- Body waves: waves which travel through the Earth's inner layers.

* Primary waves (P-waves)
It's the fastest kind, it can move through solid rock and fluids. It squishes and streches the rock it moves through ( like sound wave which compress and expand the air).

* Secondary waves (S-waves)
It's the second wave to arrive after an Earthquake and is 1.7 time slower than a P-wave. It can move only in solids. It's a transversal waves.

- Surface waves : waves wich travel along the surface of the planet. It's easily distinguished on a sismogram. A shallow earthquake produce stronger S-waves and strengh are reduced in deeper earthquakes.

* Love waves
It's entirely horizontal motion and have a largest amplitude at the surface and it decreasing with greater depth.

* Rayleigh waves
It rolls like waves on an ocean and it move the ground up, down, forward and backward. It provoques shaking felt and like the love waves, the amplitude decreasing with depth.

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d = c x Δt / 2

With:

-         d the distance

-         c the velocity of the light (8,0.10 ³ m.s⁻¹) 3,0.10 ⁸ m/s

-         Δt the duration between 2 impulsions

-         We divide by 2 because Δt is the duration for a return trip

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A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain and receiving antenna. Electromagnetic waves don’t need a medium and then they are used in spacefield because there’s not air in space.

The radar system sends an electromagnetic wave in all directions, when the wave hurts(?) an object, the wave is sent back to the rotative antenna: that’s named the radar sounding principle. To know the distance from the object, the radar calculates the time from the emission to the reception of the electromagnetic wave.

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The radar system has been invented in 1904 by Christian Hülsmeyer. The name “radar” comes from Radio Detection And Ranging. We use it for boats, planes and so on to determine the distance,the angle or the velocity of objects.

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Sonars were invented during the first world war by the two french ingeniors Constantin Chillowski and paul Laugevin in collaboration with the canadian Boyle. The goal search was just the detection of immersed obstacles. During the Second world war, The Canadian Royal Marine upgrade sonar's technology because they were responsable for ecorting sea convoys and combatting submarines.

Today, sonars are very performant and very used. the different utilities are :
- The war marine, so the detection of submarines and mines and the torpedo guidance,
-fishing, so the detection of the shoal of fish,
-maritim and river navigation to map the sea bed,
- for underwater archeology,
-and for underwater pollutions sensors.

But the main utility is to locating the bottom of the sea

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Vocabulary : vagues : waves
marée basse/haute : low/high tide
littoral : coastline
houle : swell

I) How and why there are waves on the sea ?

. because of the friction between wind and surface water.
. because of the energy of the wind
. waves transmit energy and not water
. waves can be created with de gravitational pull of the    moon  and the sun whih creates tides

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The seismic waves are generated by the movements of the Earth's tectonic plates and caused by the sudden movement of materials within the Earth such as volcanic eruptions or avalanches.

There are different kinds of seismic waves:

- Body waves
* Primary waves
* Secondary waves

- Surface waves
* Love waves
* Rayleigh waves

There are also several types of interactions between waves and the subsurface geology (rocks), are commonly obervable on sismograms. We will examine 2 simplest types of interactions:

- Refraction
- Reflection

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The sonar works using sound propagation through water : It is used to naviguate by measuring distances in the ocean, the deepth, the gap... It mesure the time between the moment the sound is launched and when it come come back to the ship and so detect danger.The sonar is also used to communicate, the ships used morse code to communicate between each other.
It is based on animals capability like dolphins or bats.
The first patent was filed right after the Titanic disaster to prevent similar catastropgic event. And so in 1913 Alexander Behm obtain the first patent.

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Humans can hear frequencies between 20 and 20 kHz, but it goes down in the old days.

Cats and dogs can hear until 40 khz, bats and dolphin until 160 khz and elephants and moles can hear infra sounds which are under 20 hz. Ultrasounds are above 20 khz.

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Pure Sounds

A sound is “pure” if its frequency is represented by a sinusoidal periodic wave.

Composed Sounds
A sound is a complex (or composed) sound if its frequency is a periodic non-sinusoidal wave. It can be deconstructed in an addition of sinusoidal waves with different frequencies. Each of these frequencies is the multiple of the a frequency said “fundamental”. These are the harmonics.

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Sound is a mechanical, a longitudinal and a pressure wave created by a vibration. It can’t propagate in vacuum, it needs a medium. Its speed depends on its medium: in the air, sound has a speed of 340 m.s⁻¹ but under water it goes at 1500 m.s⁻¹.
It can be quantified with an intensity I.

Sound Level
The easiest way to compare intensities is to use the sound level (or noise level), in dB. To go from L to I, we use this formula:

L=10 log (I/I ₀), with I ₀=10⁻¹² W.m⁻².
We can hear sounds above 0 dB but after 90dB it can be dangerous and after 120dB, it’s hurtful.

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Wavelength λ

Distance travelled by the wave before it repeats itself. Audible sounds usually represent waves of almost 17m to 1.7 centimeters (in the air).

Period T

Time requested for a complete wave cycle.

Frequency f

If a sound stays unchanged long enough, then it can be associated to a frequency (f). Its frequency is in Hertz and corresponds to the number of vibrations per second. f=1/T

Then, we can tell two types of sounds: